如何同时下载多个网址？

Question

Public Class Form1
    For i As Integer = 0 To RichTextBox1.Lines.Length - 1
        wreq=System.Net.WebRequest.Create("i  th Internet address")
        wreq.AutomaticDecompression = Net.DecompressionMethods.GZip
        wres = wreq.GetResponse
        Dim s As System.IO.Stream = wres.GetResponseStream
        Dim sr As New System.IO.StreamReader(s)
        html = sr.ReadToEnd
        s = html.Split(";")
        'here is other codes
    Next
End Class

这是我计划的一部分。我用这个的时候，大家下载好久。如何同时下载所有地址？

我在网上找到了下面的代码enter code here to do this，但我不知道如何在我的程序中使用它。请帮忙。谢谢。

Imports System.Threading.Tasks
Imports System.Net
Imports System.IO
 
Public Class Form1
 
    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        'Start a background task so as not to freeze up the UI.
        Me.BackgroundWorker1.RunWorkerAsync()
    End Sub
 
    Private Sub BackgroundWorker1_DoWork(sender As System.Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
        Dim files As String() 'Get file paths.
 
        'Download multiple files simultaneously.
        Parallel.ForEach(files,
                         Sub(f) Call New WebClient().DownloadFile(f,
                                                                  Path.Combine("local folder here",
                                                                               Path.GetFileName(f))))
    End Sub
 
    Private Sub BackgroundWorker1_RunWorkerCompleted(sender As Object, e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
        MessageBox.Show("All files downloaded")
    End Sub
 
End Class

Answer 1

看看这个。可能是一个好的开始（在每个方法上实现的部分代码）。

 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim urls() As String = RichTextBox1.Lines.Select(Function(url) Trim(url))
        Parallel.ForEach(urls, Sub(f)
                                   If Not String.IsNullOrEmpty(f) Then
                                       DownloadAsync(f)
                                   End If
                               End Sub)
 End Sub



Function DownloadAsync(URL As String) As Task(Of Boolean)

    Try
        ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12
        Dim html As String = ""
        Dim result As Boolean
        Dim request As HttpWebRequest = HttpWebRequest.Create(URL)
        request.AutomaticDecompression = DecompressionMethods.GZip
        request.Timeout = 500

        request.Method = "GET"
        request.UserAgent = "Mozilla/5.0 (Macintosh; Intel Mac OS X x.y; rv:42.0) Gecko/20100101 Firefox/42.0"

        Using response As Task(Of WebResponse) = request.GetResponseAsync
            If response.Result IsNot Nothing Then
                Using ioStream As IO.Stream = response.Result.GetResponseStream
                    Using sr As New System.IO.StreamReader(ioStream)
                        html = sr.ReadToEnd
                        Dim s() As String = html.Split(";"c)
                        For Each sl In s
                            Debug.WriteLine(sl)
                        Next
                    End Using
                    result = True
                End Using
            End If
        End Using

        Return Task.FromResult(result)

    Catch ex As Exception
        Debug.WriteLine(ex.Message)
    End Try

    Return Task.FromResult(False)

End Function

如何同时下载多个网址？

How to download multiple URLs at the same time?

vb.net

backgroundworker

parallel.foreach